Screen display control device

BACKGROUND

1. Technical Field

The present invention relates to a technique capable of controlling screen display.

2. Related Art

In the past, a screen display control device having a function of processing image data, which is disclosed in JP-A-2007-264572 (paragraphs 0017 and 0018, FIG. 1, etc.), for example, was known. The screen display control device generally includes an image memory (video RAM) temporarily storing the processed image data and performs screen display by periodically reading the processed image data stored in the image memory. In recent years, however, a screen display apparatus such as a liquid crystal display, a plasma display, or an organic EL display has a capability to realize high definition and high gray scale, thereby increasing a volume of image data to be displayed in the screen display apparatus. Therefore, the image memory storing the increased volume of image data needs to have a large capacity, thereby causing an increase in manufacture cost. As a method of solving this problem, a technique capable of compressing the image data by a known data compression method such as a predictive encoding (DPCM encoding) method of encoding differences of adjacent pixel data and storing the compressed data in the image memory was suggested. In addition, upon performing screen display, original image data is restored by reading the compressed data from the image memory and decompressing the compressed data.

However, for example, when the image data are compressed in a line unit and the compressed data are stored in the image memory, processes of writing and reading the compressed data to and from the image memory in a line unit are performed. Since the processes of writing and reading the compressed data are performed asynchronously, a line of the compressed data to be written to the image memory and a line of the compressed data to be read from the image memory are the same in some cases. When the process of writing the compressed data to the image memory and the process of reading the compressed data from the image memory are performed on the same line, the following problems may occur. That is, the process of writing newly compressed data is performed ahead during the process of reading the compressed data stored in the image memory, or the process of reading the compressed data is performed ahead during the process of writing newly compressed data to the image memory. The image data are compressed using the differences of the adjacent data, as described above. Therefore, when the writing process is performed ahead or the reading process is performed ahead, the image data are not able to be restored after the above problem occurs even in the process of reading the compressed data. In order to solve this problem, there is a known a technique in which the newly compressed data to be written are temporarily maintained in a buffer memory and the newly compressed data maintained in the buffer memory are written to the image memory after the process of reading the compressed data from the image memory is completed, when the process of writing the compressed data to the image memory and the process of reading the compressed data from the image memory are performed on the same line. However, this technique has a problem since efficiency is poor in that the newly compressed data are not able to be written to the image memory until the process of reading the already compressed data from the image memory is completed after maintaining the newly compressed data in the buffer memory. Therefore, an improved technique is necessary.

SUMMARY

An advantage of some aspects of the invention is that it provides a technique capable of efficiently writing compressed data to an image memory.

According to an aspect of the invention, there is provided a screen display control device including: a compression unit which compresses input image data in a line unit; a rewritable image memory to which the compressed data compressed in the line unit by the compression unit is written in non-synchronization with a reading process; a decompression unit which decompresses the compressed data periodically read from the image memory in synchronization with screen display to restore original image data; a display unit which displays an image of the image data decompressed and restored by the decompression unit; a buffer memory which temporarily maintains one-line data of the image data; and a writing/reading control unit which controls the process of writing the compressed data to the image memory and the processes of writing and reading the image data to and from the buffer memory. When the processes of reading and writing the compressed data of the same line to and from the image memory compete with each other, the writing/reading control unit controls the image data of the line to be written so as to be maintained in the buffer memory. In addition, the writing/reading control unit controls the compressed data of the line formed by allowing the compression unit to compress the image data maintained in the buffer memory so as to be written to a vacant area of a pixel unit generated in the image memory in a pixel unit in response to the process of reading the compressed data of the line.

In the screen display control device according to this aspect of the invention, when the processes of writing and reading the compressed data of the same line to the image memory compete with each other, the writing/reading control unit performs controls the image data of the line to be written so as to be maintained in the buffer memory and controls the process of writing the compressed data of the line formed by allowing the compression unit to compress the image data maintained in the buffer memory so as to be written to the vacant area of a pixel unit generated in the image memory in a pixel unit in response to the process of reading the compressed data of the line. Accordingly, since the process of writing newly compressed data to the vacant area generated in the image memory in a pixel unit without waiting end of the process of reading the compressed data of the line where the competition between the writing and reading processes from the image memory, it is possible to effectively write the compressed data to the image memory.

In the screen display control device, the buffer memory may be a line buffer memory which is provided in front of the compression unit to maintain the image data. With such a configuration, since a practical configuration of the buffer memory is realizable, it is possible to allow the writing/reading control unit to easily control the processes of writing and reading the image data to and from the buffer memory.

According to another aspect of the invention, there is provided a screen display control device including: a compression unit which compresses input image data in a line unit; a rewritable image memory to which the compressed data compressed in the line unit by the compression unit is written in non-synchronization with a reading process; a decompression unit which decompresses the compressed data periodically read from the image memory in synchronization with screen display to restore original image data; a display unit which displays an image of the image data decompressed and restored by the decompression unit; a buffer memory which temporarily maintains one-line data of the compressed data; and a writing/reading control unit which controls the process of writing the compressed data to the image memory and processes of writing and reading the image data to and from the buffer memory. When the processes of reading and writing the compressed data of the same line to and from the image memory compete with each other, the writing/reading control unit controls the compressed data of the line to be written so as to be maintained in the buffer memory. In addition, the writing/reading control unit controls the compressed data of the line maintained in the buffer memory so as to be written to a vacant area of a pixel unit generated in the image memory in a pixel unit in response to the process of reading the compressed data of the line.

In the screen display control device according to this aspect of the invention, when the processes of writing and reading the compressed data of the same line to and from the image memory compete with each other, the writing/reading control unit performs controls the image data of the line to be written so as to be maintained in the buffer memory and controls the process of writing the compressed data maintained in the buffer memory so as to be written to the vacant area of a pixel unit generated in the image memory in a pixel unit in response to the process of reading the compressed data of the line. Accordingly, since the process of writing newly compressed data to the vacant area generated in the image memory in a pixel unit without waiting end of the process of reading the compressed data of the line where the competition between the writing and reading processes from the image memory, it is possible to effectively write the compressed data to the image memory.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

<figref idrefs="DRAWINGS">FIG. 1</figref> is a perspective view illustrating a photo printer equipped with a screen display control device according to the invention.

<figref idrefs="DRAWINGS">FIG. 2</figref> is a diagram illustrating an overall internal configuration of the photo printer.

<figref idrefs="DRAWINGS">FIG. 3</figref> is a block diagram illustrating the configuration of a controller.

<figref idrefs="DRAWINGS">FIGS. 4A and 4B</figref> are diagrams illustrating the configurations of a display unit and a VRAM, respectively.

<figref idrefs="DRAWINGS">FIG. 5</figref> is a diagram illustrating timings at which compressed data is written and read.

<figref idrefs="DRAWINGS">FIG. 6</figref> is a diagram illustrating an example of writing prohibition determination.

<figref idrefs="DRAWINGS">FIG. 7</figref> is a diagram illustrating an example of a reading process.

<figref idrefs="DRAWINGS">FIG. 8</figref> is a diagram illustrating an example of a writing process.

<figref idrefs="DRAWINGS">FIG. 9</figref> is a diagram illustrating a back porch process.

<figref idrefs="DRAWINGS">FIG. 10</figref> is a diagram illustrating an active area process.

<figref idrefs="DRAWINGS">FIG. 11</figref> is a diagram illustrating a first front porch process.

<figref idrefs="DRAWINGS">FIG. 12</figref> is a diagram illustrating another example of the writing process.

<figref idrefs="DRAWINGS">FIG. 13</figref> is a diagram illustrating a second front porch process.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

<figref idrefs="DRAWINGS">FIG. 1</figref> is a perspective view illustrating a photo printer equipped with an LCD controller <b>76</b>, which is an example of a screen display control device according to the invention. <figref idrefs="DRAWINGS">FIG. 2</figref> is a diagram illustrating an overall internal configuration of the photo printer. A photo printer <b>10</b> has a printing mechanism <b>50</b> (see <figref idrefs="DRAWINGS">FIG. 2</figref>) inside a printer body <b>12</b> and prints an image on a paper sheet P in accordance with an operation command from a controller <b>70</b> (see <figref idrefs="DRAWINGS">FIG. 2</figref>) which controls the photo printer <b>10</b> on the whole. In addition, the printed paper sheet is discharged to a front surface of the printer body <b>12</b>.

A front door <b>14</b> is openably mounted on the front surface of the printer body <b>12</b>, as shown in <figref idrefs="DRAWINGS">FIG. 1</figref>. The front door <b>14</b> is a cover used to open and close the front surface of the printer body <b>12</b>. When the front door <b>14</b> is opened, the front door <b>14</b> functions as a sheet discharging tray which receives the paper sheet P discharged from the print mechanism <b>50</b>. In addition, a user is able to use various types of a memory card slot <b>16</b> formed on the front surface of the printer body <b>12</b>. That is, when the front door <b>14</b> is opened, the user is able to insert a memory card M storing an image file, which is a printing target, into the memory card slot <b>16</b>. An external medium storing an image file is not limited to the memory card, but may be a USB memory, a disk medium, or the like. An electronic apparatus such as a digital camera or a cellular phone storing images is connected to the photo printer <b>10</b> through a cable or infrared rays to function as the external medium.

An operational panel <b>20</b> is provided on the upper surface of the printer body <b>12</b> and a cover <b>30</b> is openably mounted on one side inside the upper surface of the printer body <b>12</b>. The cover <b>30</b> is a resin plate formed with a size covering the upper surface of the printer body <b>12</b> and the surface of the operational panel <b>20</b> is exposed to the outside (see <figref idrefs="DRAWINGS">FIG. 1</figref>). On the other hand, when the cover <b>30</b> is closed, the cover <b>30</b> covers the entire operational panel <b>20</b>.

The operational panel <b>20</b> includes a display unit <b>22</b> which is configured by as an LCD display displaying texts, figures, symbols, and the like and a group of buttons <b>24</b> arranged around the display unit <b>22</b>. As shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, the group of buttons <b>24</b> includes: a power button <b>24</b><i>a </i>used to turn on and off a power source; a menu button <b>24</b><i>b </i>used to allow a main menu to be displayed on a screen; a cancel button <b>24</b><i>c </i>used to cancel an operation during performing the operation or interrupt a printing process on the paper sheet P during the printing process; a print button <b>24</b><i>d </i>used to instruct a print execution onto the paper sheet P; a store button <b>24</b><i>e </i>used to store an edited image to the memory card M inserted into the memory card slot <b>16</b>; upper, lower, right, and left arrow buttons <b>24</b><i>f </i>to <b>24</b><i>i </i>used to select a desired option among plural options displayed on the display unit <b>22</b>, move a cursor, or other operations; an OK button <b>24</b><i>j </i>disposed in the center of the upper, lower, right, and left arrow buttons <b>24</b><i>f </i>to <b>24</b><i>i </i>and used to instruct the option selected by the arrow buttons <b>24</b><i>f </i>to <b>24</b><i>i; </i>a display switch button <b>24</b><i>k </i>used to switch screen display on the display unit <b>22</b>; a left guide selection button <b>24</b><i>l </i>used to select a left guide displayed on the display unit <b>22</b>; a right guide selection button <b>24</b><i>m </i>used to select a right guide displayed on the display unit <b>22</b>; and a sheet discharging tray opening button <b>24</b><i>n </i>used to open the front door <b>14</b> functioning as a sheet discharging tray.

In order to confirm display details of the display unit <b>22</b>, a window <b>32</b> having the same size as that of the display unit <b>22</b> is provided in the cover <b>30</b>. That is, when the cover <b>30</b> is closed, the user is able to confirm the display details of the display unit <b>22</b> through the window <b>32</b>. On the other hand, when the cover <b>30</b> is opened, the display unit <b>22</b> is configured so as to adjust a desired angle as shown in <figref idrefs="DRAWINGS">FIG. 1</figref>.

When the cover <b>30</b> is opened, the cover <b>30</b> is configured so as to be inclined toward the rear side with respect to the operational panel <b>20</b> to be maintained and used as a tray supplying the paper sheet P to the printing mechanism <b>50</b>. Inside the operational panel <b>20</b>, a sheet feeding port <b>58</b> of the printing mechanism <b>50</b> is provided and a pair of sheet guides <b>59</b> operated in a slide manner in right and left direction so that a guide width is matched with the width of the paper sheet are also provided.

The paper sheet P is fed to the printing mechanism <b>50</b> through the sheet feeding port <b>58</b> to perform the printing process. As shown in <figref idrefs="DRAWINGS">FIG. 2</figref>, the printing mechanism <b>50</b> is provided with a carriage <b>53</b> which is driven by timing belt <b>51</b> suspended in a loop shape in left and right directions to reciprocate in the right and left direction along a guide <b>52</b>. The carriage <b>53</b> is provided with a sheet end detecting sensor <b>57</b> which detects the upper, lower, right, and left ends of the paper sheet P. That is, the sheet end detecting sensor <b>57</b> is capable of detecting the right and left ends of the paper sheet P to recognize the width of the paper sheet P or detecting the rear end of the paper sheet P during the printing process to recognize the length of the paper sheet P, when the carriage <b>53</b> scans the paper sheet P fed to the sheet feeding port <b>58</b> the right and left directions before the printing process.

Ink cartridges <b>54</b> individually containing colors such as cyan, magenta, yellow, and black are mounted on the carriage <b>53</b>. The ink cartridges <b>54</b> are connected to a printing head <b>55</b>. In addition, the printing head <b>55</b> ejects ink from nozzles (not shown) onto the paper sheet P by pressurizing ink from the ink cartridges <b>54</b>. In this embodiment, the printing head <b>55</b> employs a method of pressurizing the ink with application of voltage to a piezoelectric element and deforming the piezoelectric element to pressurize the ink, but may employ a method of applying voltage to a heating resistant member (for example, a heater) and heating the ink to pressurize the ink by bubbles. The paper sheet P subjected to the printing process is transported to the opened front door (sheet discharging tray) <b>14</b> by a transport roller <b>56</b>.

Even though not shown in the drawing, a battery pack is configured to be mounted in the rear surface of the printer body <b>12</b> to allow the battery pack to operate the photo printer <b>10</b> without connecting the photo printer <b>10</b> to a commercial power source. The photo printer <b>10</b> is able to be carried with ease and used anywhere, since the photo printer <b>10</b> is operated by the battery back and used as a stand-alone printer which does not need to be connected to a host computer.

<figref idrefs="DRAWINGS">FIG. 3</figref> is a block diagram illustrating the configuration of the controller <b>70</b>. <figref idrefs="DRAWINGS">FIGS. 4A and 4B</figref> are diagrams illustrating the configurations of the display unit <b>22</b> and the VRAM <b>766</b>, respectively. As shown in <figref idrefs="DRAWINGS">FIG. 3</figref>, the controller <b>70</b> is configured as a micro processor operated mainly by a CPU <b>71</b> and includes a ROM <b>72</b> which stores various processing programs, various data, various programs, various tables, and the like, a RAM <b>73</b> which temporarily stores data, and an interface (I/F) <b>74</b> which enables the printing mechanism <b>50</b> and the memory card slot <b>16</b> to communicate with each other. In addition, the controller <b>70</b> stores an edited image or the like to the memory card M and outputs a control signal to the printing head <b>55</b> of the printing mechanism <b>50</b> or a control signal to the display unit <b>22</b> of the operational panel.

The controller <b>70</b> is provided with an image processing module <b>75</b> which performs necessary image processing on image data supplied from an external storage medium such as the memory card M through the interface <b>74</b>. The image processing module <b>75</b> has a function of generating the image data corresponding to an image proper to a printer, such as a menu screen, for displaying the image data on the display unit <b>22</b>.

RGB image data output from the image processing module <b>75</b> are supplied to the LCD controller <b>76</b> (corresponding to “a screen display control device”<b>8</b> according to the invention) which controls displaying of the display unit <b>22</b>. Hereinafter, the display unit <b>22</b> configured by an LCD display has pixels of 320 dots×240 dots of a QVGA (Quarter Video Graphics Array) mode. One line of image data is formed by image data corresponding to 320 dots and one image is formed by line data corresponding to 240 lines (see <figref idrefs="DRAWINGS">FIG. 4A</figref>).

The LCD controller <b>76</b> includes a synchronous signal generation unit <b>769</b> which generates horizontal and vertical synchronous signals for controlling timing at which an image is displayed on the display unit <b>22</b> and various synchronous signals. In addition, the LCD controller <b>76</b> includes an input data conversion unit <b>761</b> which converts serial data input from the image processing module <b>75</b> into parallel data and a line buffer <b>762</b> (corresponding to “a buffer memory” according to the invention) which temporarily maintains one-line data of the image data converted into the parallel data by the input data conversion unit <b>761</b>. In addition, the LCD controller <b>76</b> includes a compression unit <b>764</b> which is provided on the rear end of the line buffer <b>762</b> and compresses the input image data in a line unit, a rewritable VRAM <b>766</b> (corresponding to “an image memory” according to the invention) to which the compressed data compressed in a line unit by the compression unit <b>764</b> are written in non-synchronization with a reading process, a decompression unit <b>767</b> which decompresses the compressed data periodically read from the VRAM <b>766</b> in synchronization with the horizontal and vertical synchronous signals of the screen display on the display unit <b>22</b> to restore an original image data, and an output data conversion unit <b>768</b> which performs data conversion to output the image data decompressed and restored by the decompression unit <b>767</b> onto the display unit <b>22</b>. With such a configuration, the image data decompressed and restored by the decompression unit <b>767</b> are output and displayed onto the display unit <b>22</b> through the output data conversion unit <b>768</b>. In this embodiment, the compression unit <b>764</b> is configured to compress the image data using difference information (accord status) of adjacent image data. However, the method of compressing image data is not limited thereto, but known various compression methods may be used. Since the method of compressing image data is a known technique, detailed description is omitted.

As shown in <figref idrefs="DRAWINGS">FIG. 4B</figref>, the VRAM <b>766</b> at least has an area in which the compressed data of 240 lines (corresponding to one image) compressed by the compression unit <b>764</b> are stored. In this embodiment, the compressed data of lines <b>0</b>, <b>1</b>, <b>2</b>, . . . , and <b>239</b> are stored in storage areas indicated by memory addresses <b>0</b>, <b>10</b>, <b>20</b>, . . . , and <b>2390</b> of the VRAM <b>766</b>, respectively. In addition, there is provided a writing/reading control unit <b>763</b> which controls a process of writing the compressed data to the VRAM <b>766</b> and processes of writing and reading the image data to and from the line buffer <b>762</b>. Timing at which the compressed data are written to the VRAM <b>766</b> is controlled by allowing the writing/reading control unit <b>763</b> to output a control command to a RAM control unit <b>765</b>.

Next, the writing/reading control unit <b>763</b> will be described in more detail. As shown in <figref idrefs="DRAWINGS">FIG. 3</figref>, the writing/reading control unit <b>763</b> includes a line determiner <b>763</b><i>a </i>which determines whether a line of the compressed data written to the VRAM <b>766</b> is the same as a line of the compressed data read from the VRAM <b>766</b> by comparison. That is, by comparing a counter value (writing line) of a writing line counter (not shown) constituted by a memory or the like to a counter value (reading line) of a reading line counter (not shown) constituted by a memory or the like, it is possible to compare the line of the written compressed data to the line of the read compressed data. In addition, the writing/reading control unit <b>763</b> includes a pixel counter determiner <b>763</b><i>b </i>which determines whether a value of a writing pixel counter (not shown) constituted by a memory or the like to a value of a reading pixel counter (not shown) by comparison. The value of the writing pixel counter is added, whenever one-pixel data are written from compressed one-line data compressed by the compression unit <b>764</b> to the VRAM <b>766</b>. In addition, the value of the reading pixel counter is added on the basis of a clock signal generated by the synchronous signal generation unit <b>769</b> in order to specify timing at which compressed one-pixel data are read from the VRAM <b>766</b>. The writing pixel counter and the reading pixel counter will be described with reference to <figref idrefs="DRAWINGS">FIG. 5</figref>.

<figref idrefs="DRAWINGS">FIG. 5</figref> is a diagram illustrating timings at which the compressed data of each line are written and read. As shown in <figref idrefs="DRAWINGS">FIG. 5</figref>, the compressed one-line data are read from the VRAM <b>766</b> during one period in which the horizontal synchronous signal is output. In the process of reading the compressed data, one period of the horizontal synchronous signal is divided into three sub-periods, that is, “a back porch period” from time at which the horizontal synchronous signal is output to time at which the process of reading the compressed data starts, “an active area period” in which the compressed data is read and the image data is output onto the display unit <b>22</b>, and “a front porch period” from time at which the process of reading the compressed data ends to time at which a subsequent horizontal synchronous signal is output. Each of the periods is a fixed value which is set in advance depending on the configuration of the resolution number of the display unit <b>22</b> or the method of compressing the compressed data stored in the VRAM <b>766</b>. Here, the reading pixel counter is reset to “0” upon starting each of the periods and is added whenever a clock signal specifying the timing at which the compressed one-pixel data generated by the synchronous signal generation unit <b>769</b> are read. Therefore, when the horizontal synchronous signal is output and the back porch period is started, a process of adding the reading pixel counter from “0” is also started. Subsequently, when the value of the reading pixel counter becomes a value preset as the back porch period, the reading pixel counter is reset to “0” and the active area period is started to actually start the process of reading the compressed data. Finally, when the value of the reading pixel counter becomes a value preset as the active area period, that is, when the process of reading the compressed one-line data is completed, the reading pixel counter is reset to “0” and the front porch period is started. In addition, the compressed one-pixel data are read, whenever the clock signal is output. A signal indicating to which period a present period belongs among the above-described three periods is output in real time from the output data conversion unit <b>768</b> to the writing/reading control unit <b>763</b>.

On the other hand, since the process of writing the compressed data to the VRAM <b>766</b> is performed in non-synchronization with the reading process described above, the process of writing the compressed data is performed irrespective of the timing at which the horizontal and vertical synchronous signals are output. Here, the reading pixel counter is reset to “0” upon starting the process of writing the compressed one-line data and the reading pixel counter is added whenever the compressed one-pixel data are written to the VRAM <b>766</b>. As shown in <figref idrefs="DRAWINGS">FIG. 5</figref>, the period in which the compressed one-line data are written to the VRAM <b>766</b> is a fixed value determined depending on the size (length of the compressed one-line data) of the display unit <b>22</b>. In addition, according to the configuration of the display unit <b>22</b>, there are two cases, that is, a case (state A) where a writing period is within one period of the horizontal synchronous signal and a case (state B) where the writing period is not within one period of the horizontal synchronous signal but extended over two periods of the horizontal synchronous signal.

The writing/reading control unit <b>763</b> includes a writing determiner <b>763</b><i>c </i>which determines whether the process of writing the compressed one-line data to be written to the VRAM <b>766</b> is prohibited at present, that is, whether the processes of writing and reading the compressed data of the same line to and from the VRAM <b>766</b> compete with each other on the basis of results determined by the line determiner <b>763</b><i>a </i>and the pixel counter determiner <b>763</b><i>b </i>and the reading period (“the back porch period”, “the active area period”, and “the front porch period”) output from the output data conversion unit <b>768</b>.

The fact that the processes of writing and reading the compressed data of the same line to and from the VRAM <b>766</b> compete with each other means that the process of writing newly compressed data of one line is performed ahead during the process of reading the compressed data of the one line stored in the VRAM <b>766</b>, or the process of reading the compressed data of one line is performed ahead during the process of writing newly compressed data of the one line to the VRAM <b>766</b>. In this embodiment, a period described below is a writing prohibition period in which this problem may occur and thus the process of writing the newly compressed data to the VRAM <b>766</b> is prohibited. Next, a process in which the writing determiner <b>763</b><i>c </i>determines whether the present period is the writing prohibition period will be described with reference to <figref idrefs="DRAWINGS">FIG. 6</figref>.

<figref idrefs="DRAWINGS">FIG. 6</figref> is a diagram illustrating an example of writing prohibition determination. As shown in <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>, the processes of writing and reading the compressed data of the same line to and from the VRAM <b>766</b> compete with each other depending on timing at which the process of writing the compressed data is started. First, a process in “the back porch period” and “the front porch period” will be described. Here, “a BP (back porch) prohibition pixel counter value” and “an FP (front porch) prohibition pixel counter value” in <figref idrefs="DRAWINGS">FIG. 6</figref> refers to a value which is preset in accordance with the length of the period in which the compressed data of one line is written to the VRAM <b>766</b>. In addition, “the BP (back porch) prohibition pixel counter value” and “the FP (front porch) prohibition pixel counter value” refers to a value in which the process of reading the compressed data of the same line from the VRAM <b>766</b> is started before completion of the process of writing the compressed data of one line to the VRAM <b>766</b>, when the process of writing the compressed data is started after the reading pixel counter value exceeds the BP prohibition pixel counter value and the FP prohibition pixel counter value (see an arrow indicating “start of writing prohibition” in <figref idrefs="DRAWINGS">FIG. 5</figref>). When the process of reading the compressed data of one line is started before completion of the process of writing the compressed data of the one line to the VRAM <b>766</b>, the process of reading the compressed data from the VRAM <b>766</b> is periodically performed in synchronization with the screen display on the display unit <b>22</b>, irrespective of the process of writing the newly compressed data to the VRAM <b>766</b>. Therefore, when the process of reading the compressed data is performed ahead during the process of writing the newly compressed data of the VRAM <b>766</b>, a problem occurs in that the processes of writing and reading the compressed data of the same line to and from the VRAM <b>766</b> may compete with each other.

In the example shown in <figref idrefs="DRAWINGS">FIG. 5</figref>, when the writing process is started after the value of the reading pixel counter value exceeds each prohibition pixel counter value, a problem occurs in that the writing process may be started at timing later than the timing pointed by the arrow of “the start of writing prohibition” in <figref idrefs="DRAWINGS">FIG. 5</figref> and in that the processes of writing and reading the compressed data compete with each other since the process of reading the compressed data of one line from the VRAM <b>766</b> is started before completion of the process of writing the compressed data of the one line to the VRAM <b>766</b> (see “possibility of competition” in <figref idrefs="DRAWINGS">FIG. 5</figref>).

Therefore, the writing determiner <b>763</b><i>c </i>determines a period in which the processes of writing and reading the compressed data of the same line to and from the VRAM <b>766</b> may compete with other, as described above, as the writing prohibition period, when the writing/reading control unit <b>763</b> is requested to write the compressed data from the line buffer <b>762</b>. In addition, the writing/reading control unit <b>763</b> prohibits the process of writing the compressed data of the line to the VRAM <b>766</b> by prohibiting the process of writing the newly compressed data to the VRAM <b>766</b> depending on a result of the writing prohibition period determined by the writing determiner <b>763</b><i>c </i>and maintaining the image data of the line to be written in the line buffer <b>762</b>.

On the other hand, during “the active area period”, a vacant area is generated in a storage area of the VRAM <b>766</b> where the compressed data of one line is stored in response to the process of reading the compressed data of the one line from the VRAM <b>766</b>. Therefore, by writing the compressed pixel data corresponding to the vacant area, that is, only the compressed pixel data which having already been read from the VRAM <b>766</b> among the newly compressed data of one line to be written to the VRAM <b>766</b>, it is possible to avoid the problem that the process of writing the newly compressed data of one line is performed ahead during the process of reading the compressed data of the one line stored in the VRAM <b>766</b>.

In this embodiment, the writing determiner <b>763</b><i>c </i>determines whether to permit the process of writing the newly compressed pixel data to the vacant area of the VRAM <b>766</b>, when the vacant area is generated. In addition, the writing/reading control unit <b>763</b> controls the process of writing the newly compressed data of one line to the vacant area of a pixel unit generated in the VRAM <b>766</b> in a pixel unit, depending on the determination result obtained by permission to write the compressed data in the vacant area of the VRAM <b>766</b> by the writing determiner <b>763</b><i>c</i>. That is, the writing/reading control unit <b>763</b> controls the process of writing the compressed pixel data, which are formed by compressing the pixel data corresponding to the vacant area by the compression unit <b>764</b> among the image data prohibited from being written to the VRAM <b>766</b> during the writing prohibition period and maintained in the line buffer <b>762</b>, to the vacant area in a pixel unit.

In this embodiment, as described above, the process of reading the compressed data from the VRAM <b>766</b> is performed in synchronization with the screen display on the display unit <b>22</b>, that is, in synchronization with the horizontal and vertical synchronous signals from the synchronous signal generation unit <b>769</b>. On the other hand, the process of writing the compressed data to the VRAM <b>766</b> is performed in non-synchronization with the process of reading the compressed data performed for the screen display. In addition, since the compressed data of each line is written to a predetermined area of the VRAM <b>766</b>, a problem occurs in that the processes of writing and reading the compressed data to and from the VRAM <b>766</b> may compete with each other, as described above. In this embodiment, the vacant area refers to an area where the compressed pixel data have already been read from the VRAM <b>766</b> in accordance with the screen display on the display <b>22</b> among the storage areas of the VRAM <b>766</b>. Since the compressed pixel data stored in the corresponding area have already been read, there is no influence on the restoration of the compressed pixel data read from the storage areas subsequent to the corresponding area of the VRAM <b>766</b> even upon writing the newly compressed pixel data to the corresponding area. Moreover, after each compressed pixel data is read from the corresponding area, the corresponding area of the VRAM <b>766</b> may be initialized or the already compressed pixel data may be maintained in the corresponding area. Upon writing the newly compressed pixel data to the corresponding area, the newly compressed pixel data may be rewritten to the already compressed pixel data. Next, an example of the reading process will be described with reference to <figref idrefs="DRAWINGS">FIG. 7</figref>. <ul><li id="ul0001-0001" num="0051">1. Example of Reading Process <br /> Reading Process </li></ul>

<figref idrefs="DRAWINGS">FIG. 7</figref> is a diagram illustrating an example of the process of reading the compressed data from the VRAM <b>766</b> to restore the image data. The reading process in <figref idrefs="DRAWINGS">FIG. 7</figref> is a process performed in synchronization with the vertical synchronous signal output every 1/60 second by the synchronous signal generation unit <b>769</b>. In addition, the process of reading the compressed data of each line from the VRAM <b>766</b> is performed in synchronization with the horizontal synchronous signal output by the synchronous signal generation unit <b>769</b>. First, when the vertical synchronous signal is output from the synchronous signal generation unit <b>769</b>, the counter value (reading line) of the reading line counter constituted by a memory or the like is set to “0” (Step S<b>1</b>). In addition, when the horizontal synchronous signal is output from the synchronous signal generation unit <b>769</b>, the counter value (reading pixel) of the reading pixel counter constituted by a memory or the like is set to “0” (Step S<b>2</b>). The reading line which is the counter value of the reading line counter refers to a value indicating a line number to be read in future from the VRAM <b>766</b> among the compressed data. The reading pixel which is the counter value of the reading pixel counter refers to a value added whenever the compressed pixel data for one pixel is read from compressed pixel data at the head of the compressed pixel data (320 data) constituting the compressed one-line data and refers to a value indicating which numbered pixel data from the head of the compressed pixel data is read to be restored.

Next, one compressed pixel data indicated by the reading line and the reading pixel is read from the VRAM <b>766</b> in Step S<b>3</b>, and each read pixel data is decompressed and restored by the decompression unit <b>767</b> (Step S<b>4</b>). Subsequently, the restored image (pixel) data in Step S<b>4</b> is output to the output data conversion unit <b>768</b> and the display unit <b>22</b> (Step S<b>5</b>). Then, one is added to the counter value of the reading pixel counter (Step S<b>6</b>), and then it is determined whether the process of reading the compressed data of one line ends (Step S<b>7</b>).

When NO is determined in Step S<b>7</b>, the processes from Step S<b>3</b> are repeatedly performed until the process of reading the compressed data of one line ends. Alternatively, when YES is determined in Step S<b>7</b>, one is added to the counter value of the reading line counter (Step S<b>8</b>), and it is determined whether the process of reading the compressed data of the whole lines ends in Step S<b>9</b>. When YES is determined in Step S<b>9</b>, the process proceeds to Step S<b>1</b>. When a subsequent vertical synchronous signal is output, the process is again performed from Step S<b>1</b>. Alternatively, when NO is determined in Step S<b>9</b>, the process is repeatedly performed from Step S<b>2</b> until the process of reading the compressed data of the whole lines ends. Next, an example of the process of writing the compressed data to the VRAM <b>766</b> will be described with reference to <figref idrefs="DRAWINGS">FIGS. 8 to 11</figref> according to this embodiment. <ul><li id="ul0002-0001" num="0055">2. Example of Writing Process</li></ul>

<figref idrefs="DRAWINGS">FIG. 8</figref> is a diagram illustrating a first writing process as an example of the writing process. <figref idrefs="DRAWINGS">FIG. 9</figref> is a diagram illustrating the back porch process.

<figref idrefs="DRAWINGS">FIG. 10</figref> is a diagram illustrating the active area process. <figref idrefs="DRAWINGS">FIG. 11</figref> is a diagram illustrating a first front porch process. The first writing process shown in <figref idrefs="DRAWINGS">FIG. 8</figref> is a process performed in a period in which the compressed data of one line is written in State A, as shown in <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>.

First Writing Process

The first writing process will be descried with reference to <figref idrefs="DRAWINGS">FIG. 8</figref>. First, when each of image data which is processed by the image processing module <b>75</b> in order to be displayed on the display unit <b>22</b> is input to the input data conversion unit <b>761</b> of the LCD controller <b>76</b>, the counter value (writing line) of the writing line counter constituted by a memory or the like is set to “0” (Step S<b>100</b>, see <figref idrefs="DRAWINGS">FIGS. 4A and 4B</figref>). That is, in a process described below, it is determined whether compressed data of a zeroth line is written to the VRAM <b>766</b>. For convenient description, the first writing process of writing the compressed data of the zeroth line will be described with reference to <figref idrefs="DRAWINGS">FIGS. 4A</figref>, <b>4</b>B, and <b>5</b>. In addition, the writing line which is the counter value of the writing line counter refers to a value indicating a line number of the image data to be written to the VRAM <b>766</b>.

Next, the image data of the zeroth line set as the writing line in Step S<b>100</b> is temporarily stored in the line buffer <b>762</b> (Step S<b>101</b>). Subsequently, the line determiner <b>763</b><i>a </i>determines whether the writing line (zeroth line) and the reading line, that is, the line from which the reading process is being performed are the same (Step S<b>102</b>). When NO is determined in Step S<b>102</b>, the writing determiner <b>763</b><i>c </i>determines that the processes of writing and reading the compressed data of the zeroth line do not compete with each other, and then a command for storing all the image data stored in the line buffer <b>762</b> to an area of memory address “0” of the VRAM <b>766</b> is issued from the writing/reading control unit <b>763</b> to the RAM control unit <b>765</b> (Step S<b>103</b>). That is, the image data of the zeroth line stored in the line buffer <b>762</b> are compressed by the compressed unit <b>764</b> and then written to the VRAM <b>766</b>.

Alternatively, when YES is determined in Step S<b>102</b>, the writing determiner <b>763</b><i>c </i>determines whether a present period is the back porch period on the basis of the signal output from the output data conversion unit <b>768</b> (Step S<b>104</b>). When YES is determined, the back porch process described below is performed (Step S<b>105</b>). Alternatively, when NO is determined in Step S<b>104</b>, the writing determiner <b>763</b><i>c </i>determines whether a present period is an active period on the basis of the signal output from the output data conversion unit <b>768</b> (Step S<b>106</b>). When YES is determined in Step S<b>106</b>, the active area process described below is performed (Step S<b>107</b>).

Alternatively, when NO is determined in Step S<b>106</b>, a first front porch process described below is performed, and then the process proceeds to Step S<b>109</b>. Then, one is added to the counter value (writing line) of the writing line counter, and it is determined whether the process of writing the compressed data corresponding to the whole lines (<b>240</b> lines) ends (Step S<b>110</b>). When YES is determined, the process ends. Alternatively, when NO is determined, the process proceeds to Step S<b>101</b>, and the same processes are repeatedly performed.

Back Porch Process

The back porch process will be described with reference to <figref idrefs="DRAWINGS">FIG. 9</figref>. First, the writing determiner <b>763</b><i>c </i>determines whether a present period is the writing prohibition period on the basis of the result determined by the pixel counter determination unit <b>763</b><i>b </i>(Step S<b>200</b>, see <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>). When NO is determined, a command for writing the image data stored in the line buffer <b>762</b> to the VRAM <b>766</b> is issued from the writing/reading control unit <b>763</b> to the RAM control unit <b>765</b> (Step S<b>201</b>). That is, when the image data of the zeroth line stored in the line buffer <b>762</b> are compressed by the compression unit <b>764</b> and written to the VRAM <b>766</b>, the process ends and proceeds to Step S<b>109</b> of <figref idrefs="DRAWINGS">FIG. 8</figref>. Alternatively, when YES is determined in Step S<b>200</b>, the process stands by until it is determined that a present period is the active period on the basis of the signal output by the output data conversion unit <b>768</b>, and then the process ends (Step S<b>202</b>). According to the back porch process, even when the reading line and the writing line are the same, the process of writing the compressed data is performed as long as the process of writing all the compressed data of one line to the VRAM <b>766</b> is possible before start of the process of reading the compressed data from the VRAM <b>766</b>. Therefore, it is possible to effectively write the compressed data to the VRAM <b>766</b>.

Active Area Process

The active area process will be described with reference to <figref idrefs="DRAWINGS">FIG. 10</figref>. First, the writing determiner <b>763</b><i>c </i>determines whether the writing process is permitted on the basis of the result determined by the pixel counter determiner <b>763</b><i>b </i>(Step S<b>300</b>, see <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>). When NO is determined, the process stands by until the writing process is permitted, that is, the vacant area is generated in the VRAM <b>766</b> (Step S<b>300</b>). Alternatively, when YES is determined in Step S<b>300</b>, that is, when the vacant area is generated in the VRAM <b>766</b>, the one-pixel image data stored in the line buffer <b>762</b> is written (Step S<b>301</b>).

Subsequently, after one is added to the value of the writing pixel counter in Step S<b>302</b>, the writing determiner <b>763</b><i>c </i>determines whether the image data remain in the line buffer <b>762</b> on the basis of the value of the writing pixel counter (Step S<b>303</b>). When NO is determined, that is, when all the one-line image data stored in the line buffer <b>762</b> are written to the VRAM <b>766</b>, the process ends. Alternatively, when YES is determined, the process proceeds to Step S<b>300</b> and the same processes are repeatedly performed until the process of writing all the image data stored in the line buffer <b>762</b> to the VRAM <b>766</b> is completed.

First Front Porch Process

A first porch process will be described with reference to <figref idrefs="DRAWINGS">FIG. 11</figref>. In a case where the length of a period in which one-line compressed data is written to the VRAM <b>766</b> is a length in State A, as in <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>, the writing process is not prohibited due to the competition between the processes of writing and reading the compressed data, when timing at which the writing process starts is in the front porch period. Therefore, as shown in <figref idrefs="DRAWINGS">FIG. 11</figref>, when the timing at which the process of writing the compressed data starts is in the front porch period, a command for writing the image data stored in the line buffer <b>762</b> to the VRAM <b>766</b> is issued from the writing/reading control unit <b>763</b> to the RAM control unit <b>765</b> (Step S<b>400</b>). That is, when the image data stored in the line buffer <b>762</b> are compressed by the compression unit <b>764</b> and written to the VRAM <b>766</b>, the process ends. <ul><li id="ul0003-0001" num="0066">3. Another Example of Writing Process</li></ul>

<figref idrefs="DRAWINGS">FIG. 12</figref> is a diagram illustrating a second writing process as another example of the writing process. <figref idrefs="DRAWINGS">FIG. 13</figref> is a diagram illustrating a second front porch process. The second writing process shown in <figref idrefs="DRAWINGS">FIG. 12</figref> is a process performed when the writing period of the compressed data of one line is in State B (see <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>). A difference between the another example (second writing process) of the writing process and the first writing process of <figref idrefs="DRAWINGS">FIG. 7</figref> is that a period in which the compressed one-line data are written to the VRAM <b>766</b> is long and timing at which the writing prohibition starts is different (see the arrow indicating “start of the writing prohibition” in <figref idrefs="DRAWINGS">FIG. 5</figref>). Specifically, the timing at which the process of writing the compressed data starts is “reading line+1=writing line”. In addition, the reading process is performed in “the front porch period”, and when “the reading pixel counter value is larger than the FP prohibition pixel counter value”, the process of writing the compressed data to the VRAM <b>766</b> is prohibited (see “State B” and “front porch period HFP” of <figref idrefs="DRAWINGS">FIG. 6</figref>). In addition, the process of writing the compressed data to the VRAM <b>766</b> is usually prohibited during the back porch period in the case of “reading line=writing line”. Therefore, the BP prohibition pixel counter value is initialized to “0”. Hereinafter, a difference from the first writing process will be described, and description of the same process is omitted. In the second writing process, the second front porch process of determining whether the process of writing the compressed data to the VRAM <b>766</b> is prohibited is additionally performed.

Second Writing Process

The second writing process will be described with reference to <figref idrefs="DRAWINGS">FIG. 12</figref>. The line determiner <b>763</b><i>a </i>determines whether the writing line and the reading line are the same in Step S<b>502</b> (Step S<b>502</b>). Since the process performed after YES is determined is the same as that in the first writing process, description thereof is omitted. Alternatively, when NO is determined in Step S<b>502</b>, the line determiner <b>763</b><i>a </i>determines whether the reading line is a line prior to the writing line by one line, that is, “reading line+1=writing line” (Step S<b>503</b>). When NO is determined in Step S<b>503</b>, the command is issued to the RAM control unit <b>765</b> and all the image data stored in the line buffer are compressed by the compression unit <b>764</b> to be written to the VRAM <b>766</b> (Step S<b>504</b>).

Alternatively, when YES is determined in Step S<b>503</b>, the writing determiner <b>763</b><i>c </i>determines whether a present period is the front porch period on the basis of the signal output by the output data conversion unit <b>768</b> (Step S<b>505</b>). When YES is determined in Step S<b>505</b>, the second front porch process described below is performed (Step S<b>506</b>). Alternatively, when NO is determined in Step S<b>505</b>, all the image data stored in the line buffer are compressed by the compression unit <b>764</b> and written to the VRAM <b>766</b> (Step S<b>504</b>). Since subsequent processes are the same as those in the first writing process, description thereof is omitted.

Second Front Porch Process

The second front porch process will be described with reference to <figref idrefs="DRAWINGS">FIG. 13</figref>. First, the writing determiner <b>763</b><i>c </i>determines whether a present period is the writing prohibition period on the basis of the result determined by the pixel counter determiner <b>763</b><i>b </i>(Step S<b>600</b>, see <figref idrefs="DRAWINGS">FIGS. 5 and 6</figref>). When NO is determined, a command for writing the image data stored in the line buffer <b>762</b> to the VRAM <b>766</b> is issued to the RAM control unit <b>765</b> (Step S<b>601</b>). That is, the image data stored in the line buffer <b>762</b> are compressed by the compression unit <b>764</b> and written to the VRAM <b>766</b>. Subsequently, the second front porch process ends and the process proceeds to Step S<b>512</b> of <figref idrefs="DRAWINGS">FIG. 12</figref>. Alternatively, when YES is determined in Step S<b>600</b>, the process stands by until it is determined that the present process is the back porch period on the basis of the signal output by the output data conversion unit <b>768</b> (Step S<b>602</b>). Then, the second front porch process ends and proceeds to Step S<b>507</b> of <figref idrefs="DRAWINGS">FIG. 12</figref>.

In the above-described embodiment, even when the writing line and the reading line are the same, the writing/reading control unit <b>763</b> controls the process of writing the compressed data of the same line, which are formed by allowing the compression unit <b>764</b> to compress the image data maintained in the buffer line <b>762</b>, in a pixel unit to the vacant area of a pixel unit generated in the VRAM <b>766</b> in response to the process of reading the compressed data of the same line. That is, by determining the period in which the one-line compressed data are written to the VRAM <b>766</b> and whether the compressed data are written in a pixel unit to the VRAM <b>766</b>, it is possible to write newly compressed data in a pixel unit to the vacant area generated in the VRAM <b>766</b> without waiting the end of the process of reading the compressed data of the line where the competition between the writing process and the reading process may occur in the VRAM <b>766</b>. Accordingly, it is possible to effectively write the compressed data to the VRAM <b>766</b>.

Since “the buffer memory” according to the invention is configured by the line buffer <b>762</b> provided in front of the compression unit <b>764</b>, a practical configuration of “the buffer memory” is able to be realized. Accordingly, it is possible to allow the writing/reading control unit <b>763</b> to easily control the processes of writing and reading the image data to and from the line buffer <b>762</b>.

The invention is not limited to the above-described embodiment, but may be modified in various forms other than the above-described embodiment without departing the gist of the invention. For example, in the above-described embodiment, the image data are temporarily maintained in the line buffer <b>762</b> before compressing the image data. However, the image data may be temporarily maintained after compressing the image data. With such a configuration, the same advantage as that in the above-described embodiment is obtained. In addition, in the above-described embodiment, the image data are compressed by the compression unit <b>764</b> after storing the image data are usually stored in the line buffer <b>762</b>. However, a configuration in which the image data or the compressed data are stored in the line buffer may provided of course, only when the processes of writing and reading the compressed data to and from the VRAM <b>766</b> compete with each other or there is a possibility that the competition between the reading process and writing process occur.

In the above-described embodiment, the ink cartridge type photo printer <b>10</b> is described as an example, but the invention may be applied to printing apparatuses such as other ink jet printers. Moreover, the invention is widely applicable to techniques for displaying an image on a screen display device such as a liquid crystal display, a plasma display, and an organic EL display.